The main components of a waterjet propulsion apparatus include a rotor (also sometimes referred to as an impeller) and a stator located downstream thereof, both of which are located within a water conduit or flowpath. At a first end of the flowpath, upstream of the rotor, is a water inlet, where water enters the flowpath for acceleration by the rotor. The accelerated water is then “straightened” by the stator, which eliminates the swirl imparted to the water by the rotor. At a second end of the conduit, downstream of the stator, is located a nozzle or water outlet, where water that has been accelerated by the rotor and straightened by the stator passes through a funnel-shaped nozzle, further increasing thrust. This thrust is used to power a water vehicle.
The rotor is turned by a shaft that is driven by the water vehicle engine. The stator is stationary. Each of these components is located within a housing, which defines the flowpath.
One problem encountered by prior art waterjet apparatuses includes cavitation. This occurs when fluctuations in the magnitude and direction of water-flow velocities causes fluctuating pressures on a blade row. If severe enough, this can reduce surface pressures on blade rows that are below the vapor pressure of water, causing the water to boil. When this occurs, bubbles of water vapor that are created on the surface of blades can coalesce into large cavities that remain attached to the blades or that may be shed from the blade surfaces and travel downstream. Where cavitation is sufficiently severe, the flow of water through the system is impeded, resulting in cavitation or thrust breakdown. Cavitation can also lead to implosion of the bubbles back into a liquid state, potentially causing physical damage to the apparatus.
It is also desired to have a waterjet propulsion apparatus that can absorb power at relatively low RPM's. Such a design offers increased efficiency and thrust.
Other deficiencies with prior art apparatuses include excessive conduit length, relatively high weight, and relatively high cost. Such features can be especially undesirable where a waterjet propulsion apparatus is intended to power a military water vehicle.
A need therefore exists for a waterjet propulsion apparatus that reduces cavitation, reduces conduit length, decreases weight, lowers cost, and improves efficiency.